We plan to continue our stopped-flow experiments on the interaction of actin, myosin and ATP extending them to higher temperatures and also using HMM as well as S-1. We also plan to perform these stopped flow measurements using a 3-syringes stopped-flow apparatus which will permit us to mix the S-1 and ATP and at varying times thereafter add the actin. This will allow us to determine rate constants in the cycle which cannot be determined using the 2-syringe apparatus. We also plan to continue our collaboration with Terrell Hill on the theoretical implication of the refractory state for models of muscle contraction.